This section provides background information related to the present disclosure which is not necessarily prior art.
Internal combustion engines operable to combust diesel fuel have been useful as prime movers for vehicles for many years. Present diesel engine applications often require custom calibration to achieve acceptable efficiencies relative to applicable regulatory standards. In one example, an emissions regulation requires greater than 95% NOx conversion.
Development of an exhaust aftertreatment system suitable for commercial sale may require testing of one or more prototype aftertreatment systems in a laboratory environment before the engine and aftertreatment designs are finalized. During design and testing phases, it may be necessary to incorporate the use of a hot flow bench or test mule engines to obtain the target exhaust conditions and subsequently calibrate a particular diesel engine.
Many exhaust aftertreatment systems inject a diesel exhaust fluid (DEF) into the exhaust that evaporates and then converts to gaseous NH3 and CO2. DEF is an aqueous urea solution typically made from 32.5 wt % urea and 67.5 wt % deionized water. DEF is used as a consumable in selective catalytic reduction (SCR) in order to lower NOx concentration in the diesel exhaust emissions from diesel engines. One known commercially available DEF is commonly referred to as AdBlue™.
Analytical methods used to measure constituents in the exhaust of an internal combustion engine downstream of an aqueous urea injection system and SCR catalyst cannot discriminate between NOx originating from the engine, and NOx originating from the oxidation of urea or NH3. Therefore, the development of a test method to achieve the goal of simultaneously distinguishing between NOx formed by combustion of fuel and NOx formed by oxidation of the reductant would be greatly advantageous to those practitioners of the art, through improved understanding of the chemistry and an accurate determination of the urea evaporation, conversion efficiency, and γ-UI (uniformity index) to assess overall system performance.